Hydraulic brake system



APlll 9 1940- H. c. BOWEN HYDRAULIC BRAKE SYSTEM Original Filed Sept.16, 1933 QQ S NQ um wf ww @GN @n /T X QNQ Patented Apr. 9, 1940 UNITEDSTATES HYDRAULIC BRAKE SYSTEM Herbert C. Bowen, Detroit, Mich., assignorto Hydraulic Brake Company, Detroit, Mich., a

corporation of California Application September 16, 1933, Serial No.689,715 Renewed June 15, 1939 14 Claims.

This invention relates to hydraulic brake systems, and more particularlyto fluid pressure de,- vices therefor.

Heretoiore in fluid brake systems having pressure devices operablethrough a foot pedal lever,

the ratio of pedal movement to uid flow changes v at a predeterminedpoint in the pedal movement to produce a greater fluid pressure Withoutproportionately greater foot pressure. The transition takes placesuddenly, with the result that there is a period immediately following,which is uncontrollable on the part of the operator. For example, assumethat a pressure of sufficient value at the point of transition to effecta deceleration of five feet per second per second, the pressure in thisinstance being compounded to effect a deceleration of ten feet persecond per second. From this it will be readily seen that no stops canbe eifected between five and ten feet per second per second. The presentinvention aims to overcome this objection.

An object of the invention is to spread the transition from low to highvpressure over a prolonged period to smooth out the operation of thesystem.

Another object of the invention is to provide a fluid pressure devicewherein simultaneously operable low and high pressure producing meansare provided.

Another object of the invention is to provide means controlled bypressure in the system for effecting gradual transition from a low to ahigh pressure.

A further object of the invention is to provide means controlled bypressure in the system for dis-associating the low pressure producingmeans from the system.

An additional object is to provide a device of the character hereindescribed which is simple and inexpensive in structure, highly eiiicientin use, positive in action, durable in service, and a generalimprovement in the art.

Other objects and advantages of the invention will appear from thefollowing description taken in connection with the drawing forming apart of this specification, and in which- Figure 1 is a verticalsectional view of a reservoir and a compound cylinder embodying theinvention. and

Figure 2 is a schematic illustration of a complete hydraulic brakeinstallation including the reservoir and cylinder.

Referring to the drawing for more specific details of the invention, I0represents the frame of a motor vehicle chassis. The frame has suitablyAsecured thereto a housing I2 including a reservoir I4 having an opentop and a drain opening I6, the drain opening being closed as by a plugI8, and the top having iitted thereon a cover plate 20 provided with afilling opening 22 closed as by a plug 24 having a vent 26.

An operating shaft 28 extending transversely through the reservoir hassuitably secured thereto, outside of the reservoir, afoot pedal lever 30connected by a return spring 32 to a xed support. The shaft 28 also hassecured thereto, within the reservoir, a lever 34 having a lateral end36 serving to transfer motion of the shaft 28 to a piston 38 operableywithin a cylinder 40.

'I'he cylinder 40 is suitably supported on the wall of the reservoiradjacent the bottom thereof with its open end extending into thereservoir. The closed end or head of the cylinder projects from the Wallof the reservoir, and is provided with an axial port 42, communicatingvwith outlets 44, 46, and 48, respectively. The outlet 44 communicateswith a pressure switch 50 connected in a circuit 52 including a battery54 and a lamp 56, the circuit being grounded as indicated at 58. Thelamp 56 is a conventional stop light such as is in general use. Theoutlets 46 and 48 are connected by fluid pressure delivery pipes or'conduits 60 and 62 and branch pressure delivery pipes to motor cylinders64 connected between the separable ends of friction elements 66 forspreading these elements into engagement with the drums 68 of wheelbrakes 10, and the friction elements of the respective brakes areconnected by retractable springs 12. e

As shown, the cylinder 40 has a double diametral bore, providing a largeand a small chamber. The larger chamber has a slot 'I4 for the receptionof the actuating lever 34, and a port 16 providing a communicationbetween the larger chamber and the reservoir, and a by-pass 18 providesa communication between the large and small chambers. The piston 38reciprocable in the cylinder 40 includes a shell 80 tted snugly in thelarger chamber of the cylinder. This shell provides a chamber 82 havingin its wall a plurality of ports 84 providing communications between thechamber and a circumferential chamber 86 communicating with a pluralityof spaced openings 88 in a piston head 90 fitted in thelarger chamber ofthe cylinder and having fitted thereon a collapsible leak-proof cup 92.The head 90 also has a passage 94 providing a communication between thechamber 82 and the larger chamber of the cylinder. y

The head 90 has formed concentrically there- Vwith a sleeve 96 ofsmaller diameter than the dif ameter of the small chamber of thecylinder. This sleeve has a head 98 fitted snugly in the small chamberof the cylinder. The head 98 has a plurality vof spaced openings |00providing communications between the small chamber of the cylinder andthe larger chamber of the cylinder, and positioned on the head 98 is acollapsible leak-proof cup |02 having an opening |04 registering withthe bore of the sleeve 96. 'I'he cup |02 is held against displacement bya coil spring |06 interposed between the cup and a valve |08 for controlof the port 42. The valve |08 has normally closed passages |09. Thespring |06 also serves to return the piston to its retracted position.

The sleeve has therein a reciprocable Vplunger ||0 having thereon aleak-proof cup I2. The plunger has a head exposed to the fluid pressurein the smaller or high-pressure chamber and an annular portion ||5exposed to the fluid pressure in the larger or low-pressure chamber. Thearea of the plunger head is approximately twothirds that of. the annularportion ||5. This plunger ||0 also carries a disk valve ||4 arranged toseat on a rubber gasket ||6 in the chamber 82 to control the passage 94.The valve 4 is normally held against its seat by a coil spring ||8interposed between the valve and a spider |20 threaded in the shell 80.The spider has thereon a sleeve |22 arranged concentrically with respectto the piston and the sleeve has therein a pressure plug |24 for thereception of the force applying end 36 of the lever 34.

Assuming thatl the system is filled with suitable liquid or fluid, upondepressing the foot pedal lever 30 the shaft 28 is moved through anangle, and this movement of the shaft is transferred through the lever34 on the shaft tothe piston 38 to move the piston into the cylinder 40.During the initial movement of the piston, pressure is received by thecup 92 on the head of the piston 90, and the fluid in the larger chamberof the cylinder is displaced through the head 98, past the cup |02thereon into the smaller chamber of the cylinder, and from thencethrough the valve |08, which prevents retrograde movement of the fluid,and through the port 42 and outlets 44, 46 and 48 communicatingtherewith.

Movement of the fluid under pressure through the outlet 44 actuates thepressure switch 50 to close the circuit 52 resulting in lighting thesignal lamp 56, and simultaneously therewith the uid moves underpressure through the outlets 46 and 48 and the de`lvery`pipes orconduits 60 and 62 connecting these outlets to the motor cylinders 64,resulting in actuation of these cylinders to spread the brake elementsB6 against the resistance of the retractor spring 12 into engagementwith the drums 68 of the brakes 10.

When the fluid in the cylinder is placed under a pressure which, whenmultiplied by the larea of the head of the plunger ||0 and the area ofthe valve ||4, is slightly in excess of the load on the compressionspring ||8, the plunger ||0 is moved to trip the valve ||4 and therebyrelieve the fluid pressure in the larger chamber of the cylinder, aportion of the fluid being returned from the larger chamber of thecylinder through the passage 94, the valve ||4, the chamber 82, and thespider |20 to the reservoir.

As the valve ||4 opens the cup |02 seals against its cylinder wall andcloses communication between the high-pressure chamber and thelow-pressure chamber. The function of maintaining pressure on the fluidin the small chamber is thus assumed by the piston head 98 and plungerl0 without appreciable loss of pressure in the high-pressure chamber andthat part of the braking system connected therewith.

It is to be noted that the plunger 0 has a head exposed to the pressurein the high-pressure chamber and an annular portion ||5 of' larger areathan the head of the plunger which is exposed to the pressure in thelow-pressure chamber. The forces exerted on these two areas by the fluidpressures in the high and low-pressure chambers act in the samedirection to crack the valve I4 against the tension of the compressionspring H8. If the piston is being advanced slowly the cracking of thisvalve will lower the pressure in the low-pressure chamber to a greaterextent than is immediately compensated for by the advance of thehigh-pressure head 98, withthe result that the valve 4 again closes andthus continues to crack and close until the pressure in thehigh-pressure chamber is high enough to create sufficient force on thehead of the plunger ||0 to overcome the force of the compression spring||8 without any assistance from the fluid in the low-pressure chamber.Thereafter this valve will remain open throughout the remainder of theadvance of the piston.

On the other hand, if the piston is being advanced with suflicientrapidity, the forward movement of the high-pressure head 98 mayimmediately build up sufficient increase in pressure in thehigh-pressure chamber to compensate for the lowering of pressure in thelowpressure chamber due to the cracking of the valve ||4, whereupon thisvalve will continue to permit slow leakage there past as the pressure inthe low-pressure chamber is gradually dissipated.

In both types of operation the object of the invention is accomplishedin that the resistance to the-advance of the low-pressure head of thepiston is gradually dissipated as the resistance to the advance of thehigh-pressure head increases and at no time is there any abrupt changein the total resistance offered by the piston to the advancing movementof the foot pedal. The operator thus has full and complete control ofthe brakes at all times.

Upon release of the applied force on the foot I pedal lever 30, thislever is returned to its norvmal position by the spring 32.

During this movement of the foot pedal lever, the piston 38 is moved toits retracted position by the return spring |06, and fluid is returnedfrom the cylinders 64 under pressure of the retractor springs 'I2connected between the friction elements 66 of the brakes 10.

Due to friction on the column of fluid in the cylinder 40 and theconduits connecting the cylinder 40 to the cylinders 64, and to thetension of the spring |06, the piston returns to its retracted positionslightly in advance of the return of the uid to the cylinder 40. Thiscauses a partial vacuum inthe cylinder 40 resulting in collapse of thecups 92 and |02 and admission of fluid from the reservoir to thecylinder.

Upon complete return of the piston to its retracted position, theby-pass 18 and the port '|6 are uncovered, whereupon further pressure inthe cylinder causes the cups to return to static condition, and anyexcess fluid returned to the cylinder 40 from the cylinders 64 passesfrom the cylinder through the by-pass 18 to the larger chamber of thecylinder, and from thence through port 16 to the reservoir.

From the foregoing it will be readily understood that the range overwhich the transition of the pressure occurs may be determined entirelyby the area of the head of the plunger H0, the range being greater whenthe area of the plunger head is small, and, `oi? course, decreasing asthe area of the plunger head increases.

Although this invention has been described in connection with certainspecific embodiments, the principles involved are susceptible ofnumerous other applications that will readily occur to persons skilledin the art. The invention is, therefore, to be limited only as indicatedby the scope of the appended claims. v

I claim:

1. A iiuid pressure mechanism of the class described, comprising acompound cylinder providing large and small bores, a supply reservoircommunicating with said cylinder, a piston having a head in each bore,means for operating said piston to create fluid pressures in said bores,a passage through the larger head, said passage leading to saidreservoir, valve means for said passage, said valve means having aseparate area exposed to the iiuid pressure in each bore,

the forces exerted on said areas acting on said valve means-in the samedirection to open said valve and thereby gradually relieve the pressurein said larger bore, independent valve and passage means movable withthe smaller head for controlling flow between said bores, means forreplenishing said cylinder from said reservoir, and a spring for urgingsaid first-named valve means to closed position.

2. A fluid pressure mechanism of the class described, comprising acompound cylinder providing large and small bores, a supply reservoircommunicating with said cylinder, a piston having a head in each bore,means for operating said piston to create fluid pressures in said bores,a passage through the larger head, said passage leading to saidreservoir, poppet valve means for said passage, said valve means havinga separate area exposed to the fluid pressure in each bore, the forcesexerted on said areas acting on said valve means in the, same directionto open said valve and thereby gradually relieve the pressure in saidlarger bore, independent valve and passage. means movable with thesmaller head for controlling `flow between said bores, means forreplenishing said cylinder from said reservoir, and a spring for urgingsaid first-named valve means to closed position.

3. A iiuid pressure mechanism of the class described, comprising acompound cylinder providing large and small bores, a supply reservoircommunicatingwithsaid cylinder, a piston'having ahead in each bore,means for operating said piston to create fluid` pressures in saidbores, a passage through the larger head, said passage leading to saidreservoir, valve means for'said passage, said valve means having aseparate area exposed to the flui'dpressure in each bore, said areasbeingof diierent sizes, the forces'exerted on said areas acting lon saidvalve means in the same direction to open said valve-,and therebygradually .relieve the pressure in said larger bore, independent valveand passage means movable tween aid bores, means forreplenishing 7saidwith tle smaller head for controlling flow becylinde from saidreservoir, and a spring for urging said rst-named valve means to closedinder comprising large and small bores, a supply reservoir communicatingwith said cylinder, a

piston in each bore, means for operating said pistons to create iiuidpressures in said bores, a

passage through the larger piston and connect-A ing said reservoir withthe larger bore, a plunger including a valve and an area exposed to thefluid pressure in` each bore, the area exposed to the fluid pressure inthe larger bore being larger `than the area exposed to the fluidpressure in the smaller bore, the forces exerted on said areas acting inthe same direction to open said valve and thereby reduce the pressureexisting in the larger bore, means for reiilling said cylinder from saidreservoir, and a spring for urging said valve to closed position.

5. A iiuid pressure mechanism of the class described, comprising acompound cylinder providing large and small bores, a supply reservoircommunicating with said cylinder, a piston having a head in each bore,means for operating said piston to create iluid pressures in said bores.a passage through the larger head, said passage leading to saidreservoir, valve means for said passage, said valve means having aseparate area exposed to the iluid pressure in each bore, the

area exposed to the fluid pressure in the smaller bore beingapproximately two-thirds of the size of the area exposed to the ilud'pressure in the larger bore, the forces exerted on said areas acting onsaid valve means in the same direction to open said valve and therebygradually relieve the pressure in said larger bore, independent valveand passage means lmovable with the smaller head for controlling flowbetween said bores, means for replenishing said cylinder from saidreservoir, and a spring for urging said rstnamed valve means to closedposition.

6. A huid-pressure device comprising a reservoir, a cylinder havingbores of different diameters, a' piston having two heads of dilierentdiameters for creating uid pressures in said bores, a sleeve connectingthe heads, a plunger movable in' said sleeve, said plunger being exposedto and urged in the same direction by fluid pressure in both of saidbores, a passage through said piston head connecting the larger borewith said reservoir, a valve movable with said plunger to open and closesaid passage, and thereby control the pressure developed in said larger'bore, and means whereby said cylinder is refilled from said reservoir.

7. A duid-pressure device comprising a reservoir, a cylinder providingbores of different diameters, a piston including ashell providing achamber, a piston head, a passage through said head communicating withthe chamber, means connecting said chamber with said reservoir, a secondhead, said heads adapted to create fluid pressure in said bores, asleeve connecting said heads, a plunger movable in the sleeve, a valvemovableV with the plunger for opening and closing said passage tocontrol the pressure developed in said larger bore, said valve beingurged toward open position by the fluid pressure existing in both ofsaid bores, and a spring in the chamber urging the valve to its seat.

8. A fluid-pressure device comprising a reservoir, a two-diametercylinder providing a pair of bores, a piston including a shell providinga chamber, a head on said shell, a. passage through said headcommunicating with the chamber,

vmeans-connecting said chamber with said reservoir, a second head, saidhead movable to create fluid pressurein said bores, n. sleeve connectingsaid heads, a plunger movable in the sleeve and acted upon in the samedirection'by the pressures in said bores, a valve movable with theplunger for opening and closing said passage to control the pressurecreated in said larger bore, a spider in the shell, a spring interposedbetween the spider and the valve, and means for replenishing saidcylinder from said reservoir.

9. A fluid-pressure device comprising a reservoir, a two-diametercylinder providing a pair of bores, a piston including a cylindricalmember having an axial bore, heads formed upon the ends of saidcylindrical member, said heads adapted to create fluid pressures in saidfirstnamed bores and having openings registering with said axial bore, askirt formed integral with one of the heads and providing a chamber, aplunger movable in said axial bore, a passage providing communicationbetween the chamber and one of the bores, a valve movable with theplunger to open and close said passage and control the pressure in saidlast-mentioned bore,

said plunger acted upon in the same direction by the pressures in bothof said first-mentioned bores, a spider secured in the chamber andpermitting communication between said chamber and said reservoir, aspring interposed between the spider and the valve, a pressure block supported by the spider, and means for relling said cylinder from saidreservoir.

10. A fluid pressure device comprising a cylinder having a doublediametral bore providing two chambers, a piston reciprocable thereinhaving spaced heads fitted in the respective chambers, and a boreextending through the respective heads, a skirt on one of the headsproviding a housing, a plunger movable in said last-named bore, saidplunger having a surface exposed to the fluid pressure in each chamberand being urged in the same direction by the action of the fluidpressures on both of said surfaces, a fluid reservoir, a passageconnecting said reservoir with the larger of said chambers, a valve insaid passage carried by said plunger, said valve controlling the releaseof pressure from said larger chamber, a member secured in said housing,a spring interposed between the member and valve, means for replenishingsaid cylinder from said reservoir, a second passage connecting saidchambers, and a second valve independent of said first-mentioned valvefor controlling said second passage.

l1. A fluid pressure device comprising a reservoir, a cylinder suppliedtherefromhaving a double diametral bore -providing a low pressurechamber and a high pressure chamber, expansible elements connected tothe high pressure chamber, brake elements actuated by the expansibleelements, a valve controlling movement of fluid from the expansibleelements to the high pressure chamber, a piston reciprocable in thecylinder having spaced heads tted in the respective chambers and anaxial bore extending through the heads, the smaller head having openingsproviding communications between the low and high pressure chambers, acollapsible cup on the smaller head controlling the opening, a kirt onthe larger head providing a housing opening into the reservoir, thelarger head having a plurality of openings providing communicationsbetween the low pressure chamber and the housing, a collapsible cup onthe larger head controlling the openings therein, a plunger movable inthe bore, said plunger having a surface exposed to the fluid pressure ineach chamber, said plunger being urged in the same direction by theaction of the fluid pressures on both oi' said surfaces, a valve carriedby the plunger, a passage providing a communication between the lowpressure chamber and the housing, said valve controlling said passage, asupport in the housing, a compression spring between the support and thevalve, a block on the support, and an actuator engaging the block.

12. A fluid system for transmitting power between a foot pedal or likeelement and a brake cylinder and acting 'in several phases withdifferent predetermined ratios of transmission, comprising a piston unithaving a large piston and a small piston, means operated by the footpedal for actuating the piston unit, a cylinder for each of saidpistons, duct means between the small cylinder and the brake cylinder, acommunication between the two cylinders, a valve in said communicationopening towards the small cylinder, a fluid reservoir, a communicationbetween the large cylinder and the fluid reservoir, a second valve insaid communication, said second valve opening under pressure in thelarge cylinder, resilient return means for said second valve, and anelement subjected to the pressure in the small cylinder and acting whenmoved under such pressure to open said second valve, said first valve,second valve and element being carried by the piston unit.

13. A fluid pressure device comprising a cylinder having a large chamberand a small chamber, a piston reciprocable in the chambers. means forby-passing fluid from the larger chamber past the piston into the smallchamber, a discharge outlet for the small chamber, means for relief ofpressure on the fluid in the larger chamber including a valve having apart subjected to pressure on the fluid in the large chamber and anotherpart of smaller area than the rst, part subjected to pressure on thefluid in the small chamber, the combined pressures acting in the samedirection on said parts and tending to open the valve, and means lurgingthe valve to close.

14. A fluid pressure device comprising a compression cylinder having alargechamber and a small chamber, a piston unit sealing with both ofsaid chambers, bypass valve means permitting flow of fluid from thelarger to the. smaller cham-v ber, a discharge outlet for the smallerchamber, said piston unit providing a passageway connecting that part ofthe larger chamber in front of the piston unit with that part of thelarger chamber in rear thereof, said piston unit comprisingspring-pressed valve means normally closing said passageway, and meansfor advancing said piston unit in said chambers to create fluidpressures therein, said last-named valve means having a part acted uponby fluid pressure in the small chamber and another part of larger areathan the first part acted upon by fluid pressure in the large chamberwhereby said valve means opens in response to the sum of the forces, asdistinguished from the difference between the forces, exerted on saidparts by the fluid pressures in the large and small chambers.

HERBERT C. BOWEN.

